Demands for various display devices have increased with development of an information society. Accordingly, many efforts have been made to research and develop various flat display devices such as liquid crystal display (LCD), plasma display panel (PDP), electroluminescent display (ELD), and vacuum fluorescent display (VFD). Some species of flat display devices have already been applied to displays for various equipment. Among the various flat display devices, liquid crystal display (LCD) devices have been most widely used due to advantageous characteristics of thin profile, lightness in weight, and low power consumption, whereby the LCD devices provide a substitute for a Cathode Ray Tube (CRT). In addition to mobile type LCD devices such as a display for a notebook computer, LCD devices have been developed for computer monitors and televisions to receive and display broadcasting signals. Despite various technical developments in LCD technology having applications in different fields, research in enhancing the picture quality of the LCD device has been, in some respects, lacking as compared to other aspects of the LCD device. In order to use LCD devices in various fields as a general display, the key to developing LCD devices depends on whether LCD devices can provide a high quality picture, such as high resolution and high luminance with a large-sized screen, while still maintaining lightness in weight, thin profile, and low power consumption.
Hereinafter, a related art LCD device and spacers for maintaining a cell gap between substrates therein will be described with reference to the accompanying drawings. FIG. 1 is an exploded perspective view illustrating a related art LCD device. The related art LCD device includes first and second substrates 1 and 2, and a liquid crystal layer 3 formed between the first and second substrates 1 and 2 by injection. In more detail, the first substrate 1 includes a plurality of gate lines 4 arranged along a first direction at fixed intervals, a plurality of data lines 5 arranged along a second direction perpendicular to the first direction at fixed intervals. A plurality of pixel electrodes 6 are arranged in a matrix-type configuration within pixel regions P defined by crossing of the gate and data lines 4 and 5. The first substrate 1 also includes a plurality of thin film transistors T for transmitting data signals from the data lines to the respective pixel electrodes according to gate pulse signals supplied to the gate lines. Also, the second substrate 2 includes a black matrix layer 7 that blocks light from portions of the first substrate 1 except the pixel regions P, an R/G/B color filter layer 8 for displaying various colors, and a common electrode 9 for producing the image on the color filter layer 8. In the aforementioned LCD device, the liquid crystal layer 3 is formed between the first and second substrates 1 and 2, wherein liquid crystal molecules of the liquid crystal layer 3 are driven by an electric field generated between the pixel electrode 6 and the common electrode 9. That is, an alignment direction of the liquid crystal molecules of the liquid crystal layer 3 is controlled by the induced electric field thereto. Accordingly, light irradiated through the liquid crystal layer 3 may be controlled by the alignment direction of the liquid crystal molecules, thereby displaying the image. This kind of LCD device is referred to as a TN mode LCD device, which has disadvantageous characteristics such as a narrow viewing angle. In order to overcome the narrow viewing angle, an IPS (In-Plane switching) mode LCD device has been developed actively. In the IPS mode LCD device, a pixel electrode and a common electrode are formed in a pixel region in parallel to each other at a fixed interval therebetween with this configuration, an electric field parallel to substrates develops between the pixel electrode and the common electrode, thereby aligning liquid crystal molecules of a liquid crystal layer to the electric field parallel to the substrates.
Hereinafter, a method of manufacturing a related art IPS mode LCD device will be described with reference to the accompanying drawings. In general, the method of manufacturing an LCD device is classified as either a liquid crystal injection method or a liquid crystal dispensing method depending upon the a method of forming the liquid crystal layer.
First, the method of manufacturing the LCD device according to the liquid crystal injection method will be described as follows. FIG. 2 is a flow chart illustrating the method of manufacturing the LCD device according to the liquid crystal injection method. The method of manufacturing the LCD device is divided into three processes an array process, a cell process, and a module process. The array process largely includes two steps of forming a TFT array (A) having gate and data lines, a pixel electrode, and a thin film transistor on a TFT substrate, and forming a color filter array (B) having a black matrix layer, a color filter layer, and a common electrode on a second substrate. During the array process, a plurality of LCD panel regions are defined on one large sized glass substrate, and the TFT array and the color filter array are formed in each LCD panel region. After that, the TFT substrate and the color filter substrate are moved to a cell process line. Subsequently, an alignment material is deposited on the TFT substrate and the color filter substrate, and an alignment process (rubbing process) (S10) is performed to the TFT and the color filter substrates to obtain a uniform alignment direction in the liquid crystal molecules. At this time, the alignment process (S10) is carried out in sequential processes for cleaning, before deposition of an alignment layer, printing the alignment layer, baking the alignment layer, inspecting the alignment layer, and rubbing the alignment layer. Accordingly, the TFT substrate and the color filter substrate are respectively cleaned (S20). Then, ball spacers for maintaining a cell gap between the two substrates are scattered on one of the two substrates (S30), and a seal pattern having an injection inlet is formed corresponding to the circumference of respective LCD panel regions to bond the two substrates to each other (S40). At this time, the seal pattern has a liquid crystal injection inlet through which liquid crystal is injected. The ball spacers are formed of plastic balls or elastic plastic minute particles. Then, the TFT substrate and the color filter substrate having the seal pattern therebetween are brought together, and bonded to each other, and then the seal pattern is hardened (S50). After that, the TFT substrate and the color filter substrate are cut into the respective LCD panel regions (S60), thereby manufacturing the unit LCD panels each having a fixed size. Subsequently, the liquid crystal is injected into the LCD panel through the injection inlet, and then the injection inlet is sealed (S70), to form a liquid crystal layer. After an inspection process (S80) for external appearance and electric failure in the LCD panel, the process of manufacturing the LCD device is completed. Following the cell process, the module process is carried out to complete fabrication of the LCD device.
The process for injecting the liquid crystal will now be described. First, the LCD panel and a container having liquid crystal material therein are provided in a chamber, and the chamber is evacuated. Moisture and air bubbles in the liquid crystal material and the container are simultaneously removed, and an inside space of the LCD panel is maintained in a vacuum state. Then, the injection inlet of the LCD panel is dipped into a container having the liquid crystal material in the vacuum state, and the vacuum state inside the chamber is brought to atmospheric pressure. Thus, the liquid crystal material is injected into the LCD panel through the injection inlet by a pressure difference between the inside the LCD panel and the chamber.
However, the method of manufacturing the LCD device by the liquid crystal injection method has the following disadvantages. First, after cutting the large sized glass substrate into the respective LCD panel regions, the injection inlet is dipped into the container having the liquid crystal material while maintaining the vacuum state between the two substrates. The process of injecting liquid crystal material between the two substrates is slow thereby lowering yield. Also in the case of forming a large sized LCD device, it is difficult to completely inject the liquid crystal material into the inside of the LCD panel, thereby causing failure due to incomplete injection of the liquid crystal material. Furthermore, the process of the liquid crystal material is slow and a large space is required for the liquid crystal injection device.
In order to overcome the problems with liquid crystal injection method, the liquid crystal dispensing method has been developed. In the dispensing method, two substrates are bonded to each other after dispensing liquid crystal material on any one of the two substrates. FIG. 3 is a flow chart illustrating a method of manufacturing an LCD device according to the liquid crystal dispensing method. Liquid crystal dispensing methods are disclosed in co-pending patent applications having Ser. No. 10/184,083, publication no. 20030145944, Ser. No. 10/184,117, publication no. 20030147039, and Ser. No. 10/10/184,076, publication no. 20030145943, all filed Jun. 28, 2002, the disclosures of which are incorporated by reference herein. In the method of manufacturing the LCD device according to the liquid crystal dispensing method, before bonding the two substrates, the liquid crystal is dispensed on either the TFT substrate or the color filter substrate. In this method, it is impossible to use ball spacers for maintaining a cell gap between the two substrates since the ball spacers move in the spreading direction of liquid crystal material. Thus, instead of the ball spacers, patterned spacers or column spacers are fixed to any one of the two substrates to maintain the cell gap between the two substrates. During the array fabrication process, a black matrix layer, a color filter layer and a common electrode are formed on the color filter substrate (not shown). Then, a photosensitive resin is formed on the common electrode and selectively removed to form the column spacers on the black matrix layer. The column spacers may be formed in a photo process or an ink-jet process. After that, alignment layers are respectively deposited on the entire surfaces of the TFT substrate and the color filter substrate including the column spacers, and a rubbing process is performed thereto (S100). After cleaning the TFT substrate and the color filter substrate (S101), the liquid crystal material is dispensed on one of the two substrates (S102), and a seal pattern is formed in the circumference of an LCD panel region on the other of the two substrates by a dispensing device (S103). At this time, it is possible to dispose the liquid crystal and form the seal pattern on any one of the two substrates. After the other substrate having no the liquid crystal material is inversed (S104), the TFT substrate and the color filter substrate are bonded to each other by pressure, and the seal patterned is hardened (S105). Subsequently, the bonded substrates are cut into the respective LCD panels (S106). Finally, an inspection process (S107) for external appearance and electric failure in the LCD panel is performed, so that the process of manufacturing the LCD device is completed.
In the method of fabricating the LCD device according to the liquid crystal dispensing method, the column spacers are formed on the color filter substrate, the liquid crystal is dispensed on the TFT substrate, and the two substrates are bonded together thereby completing the LCD panel. At this time, the column spacers are fixed on the color filter substrate, and the color filter substrate is in contact with the TFT substrate. Then, the contact portion of the TFT substrate has a predetermined height from the color filter substrate corresponding to any one line of the gate and data lines. Meanwhile, in case of the large sized LCD device, the liquid crystal dispensing method is generally used due to advantageous characteristics such as decreased fabrication time. At this time, the amount of liquid crystal dispensed on the LCD panel is a very important factor in the performance of the LCD panel. Especially, if excess liquid crystal is dispensed on the LCD panel, the LCD device may have gravity defects. In this case, it is necessary to repair the gravity defect of the LCD device since the gravity defect may cause failure of the LCD device after the bonding process of the substrates. This problem has not been solved.
Hereinafter, gravity defects will be described with reference to the accompanying drawings. FIG. 4 is a photograph of a gravity defect in an LCD device according to the related art. FIG. 5 is a cross sectional view taken along section line I-I′ of FIG. 4. As show in FIG. 4, a gravity defect (inducted by the widened area of the right hand side of the figure) arises at a lower corner of the LCD panel, adjacent to the ground. For example, when the LCD panel is maintained in a vertical direction, liquid crystal molecules of the LCD panel migrate to the lower corner direction, thereby causing the gathering of liquid crystal molecules to the predetermined portion on the LCD panel due to the effects of gravity. As a result, the gathered liquid crystal molecules are expanded as the temperature increases, so that a portion of the LCD panel, adjacent to the ground protrudes.
If the LCD panel is maintained at a normal temperature, even though the liquid crystal molecules migrate to the lower corner direction, the gravity defect does not affect the LCD panel the lower and upper substrates are spaced from each other at a height corresponding to the column spacer, and the liquid crystal is formed at a height corresponding to the column spacer between the two substrates. However, when the LCD panel is maintained at a high temperature, the liquid crystal at the lower corner of the LCD panel adjacent to the ground is saturated and expands with the rise in the temperature. The expanded liquid crystal portion increases the cell gap. Accordingly, if the LCD panel has a gravity defect, there is a difference of light transmission between the portion having a normal cell gap and the lower corner of the LCD panel adjacent to the ground, and opaque spots occur at the corner of the LCD panel.
In the cross section of the LCD panel 10, as shown in FIG. 5, the column spacers 30 provided at the lower corner of the LCD panel 10 come apart from the lower substrate 1, due to expansion of liquid crystal. As a result, it is impossible to support the lower and upper substrates 1 and 2 with the column spacers 30 at the lower corner of the LCD panel 10. Especially, as shown in FIG. 4 and FIG. 5, if the liquid crystal is excessively dispensed on the LCD panel 10 when maintaining the LCD panel 10 in a vertical orientation, the liquid crystal flows to the lower corner of the LCD panel 10 due to gravity, thereby increasing the size of the protruding portion at the lower corner of the LCD panel.
At this time, the seal pattern 25 is formed in the circumference of the LCD panel 10, to bond the lower and upper substrates 1 and 2 to each other. Then, the liquid crystal layer 3 is formed between the lower and upper substrates 1 and 2 with the dispensed liquid crystal. In this liquid crystal layer 3, the cell gap of the portion having the gravity defect is different from the cell gap of the portion having no gravity defect.
FIG. 6 is a plane view of an LCD panel of an LCD device according to the related art and FIG. 7 is a cross sectional view taken along Section line II-II′ of FIG. 6.
Referring to FIG. 6, an LCD panel 10 of an LCD device according to the related art includes a lower substrate 1 having a thin film transistor array, an upper substrate 2 leaving a color filter array in opposite to the lower substrate 1, and a liquid crystal layer 3 (FIG. 5) between the lower and upper substrates 1 and 2. In to allow a margin for connection with a driving part, the lower substrate 1 is relatively larger than the upper substrate 2.
The LCD panel 10 is defined as a display area (area within a dotted line) for displaying substantial images, and a non-display area (outside the dotted line) around the display area. In the non-display area of the LCD panel, a seal pattern 25 is formed to bond and support the two substrates 1 and 2. In the non-display area inside the seal pattern 25, a liquid crystal margin region is formed. Also, a black matrix layer (not shown) is formed on the upper substrate 2 in the non-display area to prevent light leakage. As described above, the black matrix layer is selectively formed in the display area.
Referring to FIG. 7, the seal pattern 25 in the non-display area is formed on any one of the lower and upper substrates 1 and 2. Then, the black matrix layer 135 is formed on the upper substrate 2 of the non-display area, to prevent light leakage. Accordingly, after bonding the lower and upper substrates 1 and 2, the seal pattern 25 is formed in correspondence with the black matrix layer 135.
Accordingly, the related art LCD device has the following disadvantages. The formation method of the liquid crystal layer between the lower and upper substrates of the LCD panel is classified into the liquid crystal injection method and the liquid crystal dispensing method. In the liquid crystal injection method, the liquid crystal is injected into the space between the lower and upper substrates of the LCD panel in the vacuum state by the capillary action. In the liquid crystal dispensing method, the liquid crystal is dispensed on the LCD panel. In the case of large sized LCD panels, the liquid crystal dispensing method is more advantageous than the liquid crystal injection method in that the liquid crystal injection method has the disadvantageous characteristics such as low yield and increased fabrication time. In the case of the liquid crystal dispensing method, the liquid crystal is dispensed on any one of the substrates at a measured amount. In this case, if the measured amount of liquid crystal dispensed on the LCD panel is incorrect due to internal changes of the LCD panel, it may have the problems. For example, if excess liquid crystal is dispensed on the LCD panel, it may cause a gravity defect. Alternatively, if the liquid crystal is deficient, it may result in poor display quality. If excessive liquid crystal is dispensed on the LCD panel, and the LCD panel is maintained at a high temperature, complete failure of the LCD panel is possible.